Question

The element lithium has bcc packing with a body-centered cubic unit cell. The volume of the unit cell is 4.32 x 10-26 L. Calculate the density (g/cm3) of the element.

Answer 1

There are two Li atoms per unit cell for a bcc structure.
mass = 2*massofmole Li/6.022 x 10^23 = mass of unit cell. You know the volume.
density = mass/volume.

Answer 2

Note that the problem asks for density in g/cc so you must change the volume in liters to cc in order to obtain the unit g/cc.